Controllable Fluids in Pipe Bending

ABSTRACT

A method for shaping partially enclosed structures such as pipes, the method comprising: filling the structure with ERF, applying an electrical field to the ERF to increase its viscosity, shaping the structure, removing the field and removing the ERF from the structure.

This invention relates to bending structures containing fluids whoseviscosity is adjustable, such as electro-rheological fluids.

In a common pipe bending method a die is pushed against the tube or pipeby a mechanical force, forcing the pipe to conform to the contours ofthe die. Lacking internal support in the pipe, this pipe bending processcreates some cross sectional reduction in the pipe. The thinner the wallof the pipe, the more deformation of the pipe is seen.

Using rotary-draw or cold form pipe bending machines, a steel plug fitsinside the pipe while a moving steel die forms the pipe to the radius ofthe die. The steel plug, or mandrel, supports the pipe internally toreduce the amount of pipe cross section flattening during pipe bending.After the pipe bending process, the mandrel is extracted from the pipeand if heated, the area is quenched by a water or air spray. With propertooling, this pipe bending process is capable of producing high quality,tight-radius bends for a wide range of applications including footballgoalposts, davit arms and pneumatic conveying systems. However suchtooling is expensive and requires experience and skill to use correctlyand its typical cost is higher than other methods.

Sand-packing and hot-slab forming starts with packing the pipe to bebent with a fine sand, then capping the ends. The pipe is placed in afurnace and heated to a high temperature. After removing it from thefurnace, the pipe is secured by one end to a bending slab. The unsecuredend of the pipe is pulled against pins in the slab until the bendassumes the desired radius. The sand minimizes cross section collapseand ovality. This is an archaic process, with sand residue oftenremaining in the internal structure of the pipe and the heat in somecase being sufficient to alter the physical structure of the sandcausing it to adhere to the pipe surface, however, many pipe bends arestill made in this fashion.

There is therefore a need for improved method of shaping pipes.

Electro-rheological fluids (ERFs) are known and are described in ourpatent application GB 0417587.3. Electro-rheological materials arematerials whose rheological properties change when an electric currentis applied. Typically the materials behave as fluids in the absence ofan electric field. When an electric field/current is applied thematerials' viscosity and shear stress at yield increase.

A number of applications have been proposed for electro-rheologicalfluids. These include use in clutches, brakes, hydraulic valves anddampers for use in applications such as engine mounts, suspension shockabsorbers and seat supports. (See for example U.S. Pat. No. 6,105,420).

In accordance with the present invention such fluids can be used forassisting pipe bending. Fluid can be introduced into a pipe and then acurrent applied to it to increase its viscosity. The pipe is then bentand the fluid will support the pipe during bending. The field can thenbe removed and the fluid can flow out of the bent pipe.

The field can be applied from electrodes at one end of the pipe to theother (if the pipe is of electrically insulating material) or from aconductor in the interior of the pipe to the pipe itself (if the pipe iselectrically conductive).

Using this method pipes of complex shapes can readily be bent in aprocess similar to sand-bending, but cold. The need for removal of theformer or support from the interior of the pipe no longer limits theshaping that can be done.

The invention is especially applicable to the shaping of vehicle exhaustpipes. Such pipes could be formed of a dual skin, with the ERF fillingthe void between the skins and thus allowing complex bends of both pipestogether, or the ERF filling the pipes entirely. Dual skins are used fora multiplicity of roles, from the lowering of thermal inertia of theinner wall, through to external heat and noise insulation. A novel usecould be that of heat exchange between the two zones thus defined, fromthe exhaust in one zone to (e.g.) heating fluid for the interior of thevehicle in the other zone.

According to the present invention there is provided a method forshaping partially enclosed structures such as pipes, the methodcomprising filling the structure with ERF, applying an electrical fieldto the ERF to increase its viscosity, shaping the structure, removingthe field and removing the ERF from the structure.

Further advantageous features are disclosed in claims 2 to 10.

An example of the present invention will now be described, withreference to the drawings.

In the drawings:

FIG. 1 shows a cross section through an unbent pipe; and

FIG. 2 shows a cross-section through a bent pipe;

FIG. 1 shows a pipe 1 with an electro-rheological fluid 5 present insidethe pipe to an extent that the fluid completely fills the pipe.Electrode 16 are attached to the pipe and these are connected via cables14 to a power supply 10, which can apply an electrical field between theelectrodes 16 on actuation of switch 12. The power supply could containa battery as a source of electrical power. When the power supply isturned off the fluid has a random structure and conforms to the insidesurface of the pipe.

FIG. 2 shows the power supply turned on. The electro-rheological fluidand the power supply are selected so that the fluid can flow readilywhen no electrical field is imposed, but so that the fluid becomessubstantially rigid when an electrical field is imposed by the powersupply. The fluid gives support to the internal structure of the pipeduring the bending process. Subsequently the field can be removed,releasing the fluid to allow it to flow out of the pipe.

Electro-rheological fluid generally comprises a carrier liquid in whichparticles are dispersed. Additives may be included to improve theperformance of the liquid. The liquid is a dielectric and could, forexample, be an oil. The particles can, for example, be based on silica,zeolites, gum Arabic, formaldehyde polymer, active carbon,poly(acenequinone) radical (PAQR) polymers, polyeurethane polymers orsurface treated carbon. When no electrical field is applied theparticles are free to move in the fluid and the fluid has a relativelylow viscosity. When an electrical field is applied across the fluid theparticles take on an ordered structure which resists flow, giving thefluid a relatively high viscosity and a relatively high shear stress atyield. By selection of the materials, the particle loading and anyadditives, the viscosity of the fluid when no field is applied, and therheological response of the fluid to the application of a field can betailored for a desired application.

The electro-rheological fluid and the power supply are selected so thatthe fluid can flow when no electrical field is imposed, but so that thefluid becomes substantially rigid (e.g. about 90% solid or above 10,000centistokes) when an electrical field is imposed by the power supply.The viscosity of the fluid when no field is imposed can be selectedbased on the application, but could be in the range from 10 to 1000centistokes.

The material with which the pipe is filled before bending behaves as anERF in that it becomes stiffer in the application of an electric fieldacross it. That material need not be a single fluid, or entirely liquid.It could be formed of a mixture of a material that behaves as an ERFwith a material that by itself does not behave as an ERF. It may be amixture of an ERF with a material (such as sand) that comprises rigidparticles. It may be a mixture of an ERF with one or more flexiblebodies. The amount of ERF that is required may be reduced by introducinga flexible body such as a plastic hose into the interior of the pipe andfilling the pipe by introducing the ERF into the region between the hoseand the pipe.

The applicant hereby discloses in isolation each individual featuredescribed herein and any combination of two or more such features, tothe extent that such features or combinations are capable of beingcarried out based on the present specification as a whole in light ofthe common general knowledge of a person skilled in the art,irrespective of whether such features or combinations of features solveany problems disclosed herein, and without limitation to the scope ofthe claims. The applicant indicates that aspects of the presentinvention may consist of any such feature or combination of features. Inview of the foregoing description it will be evident to a person skilledin the art that various modifications may be made within the scope ofthe invention.

1. A method for shaping a partially enclosed structure, the methodcomprising the steps of: filling the structure with ERF, applying anelectrical field to the ERF to increase its viscosity, shaping thestructure, removing the field and removing the ERF from the structure.2. The method for shaping a partially enclosed structure according toclaim 1, wherein the structure is an electrically insulating materialand the field is applied from electrodes at one end of the structure tothe other.
 3. The method for shaping a partially enclosed structureaccording to claim 1, wherein the structure is electrically conductiveand the field is applied from a conductor in the interior of thestructure to the structure itself.
 4. The method for shaping a partiallyenclosed structure according to claim 1, wherein the ERF comprises adielectric.
 5. The method for shaping a partially enclosed structureaccording to claim 4, in which the liquid is wherein the dielectric isan oil.
 6. The method for shaping a partially enclosed structureaccording to claim 1, wherein additives are included in the ERF toimprove the performance of a liquid in the ERF.
 7. The method forshaping a partially enclosed structure according to claim 1, wherein theERF comprises particles based on a material selected from the groupconsisting of silica, zeolites, gum Arabic, formaldehyde polymer, activecarbon, poly(acenequinone) radical (PAQR) polymers, polyeurethanepolymers and surface treated carbon.
 8. The method for shaping apartially enclosed structure according to claim 1, wherein the ERF has alow viscosity when particles in the ERF are free to flow.
 9. The methodfor shaping a partially enclosed structure according to claim 1, whereinthe ERF becomes substantially rigid when the electrical field is imposedby a power supply.
 10. (canceled)
 11. The method for shaping a partiallyenclosed structure according to claim 1, wherein the structure is apipe.